Re: Fuel pump and filter mystery

On Oct 30, 11:08 am, "Roger Long" <stri...@xxxxxxxxxxxx> wrote:
I had a little S&L moment and my first experience with a clogged fuel filter
on my cruise this last weekend and I'm still not quite clear about what
happened.

I was motoring along on the second day when I heard the engine hesitate just
for a moment. I put the throttle up to full and, sure enough, the RPM's
didn't increase. Moments later, the RPM's started dropping steadily. You
folks who said the failure would come on fast were right I thought to
myself. I set sail and cleared some nearby ledges and then hove to for
filter replacement.

The sediment bowl and the fuel drained out of it into a clear soda bottle
were absolutely pristine. I changed the primary filter and then pressed the
push button switch on the Stewart Warner fuel lift pump to bleed the system.
Nothing. I opened up the primary fuel filter housing again to be sure there
was no back pressure to keep the pump turned off. It wouldn't come on. I
figured I had a fuel pump failure. I also realized that a spare fuel pump
had slipped my mind. I phoned ahead to the yard in Boothbay and sailed in
to find an automotive pump from NAPA waiting.

Before putting the new pump in, I checked the electrical connections to the
fuel pump. Everything was solid. I pressed the button and the pump
started! There are two entirely separate electrical pathways to this pump,
one through the starter key switch and one through the direct wired
pushbutton for bleeding. Neither made the pump run after I changed the
filter.

I started the engine and motored over to the marina to top off the half
empty tank. On the way, I did the full power test and the engine wouldn't
come up above cruise. It also hesitated a couple of times. After fueling,
I changed the secondary filter. I run 2 micron elements in the primary so
it should have been OK and it looked very clean. After changing it however,
the engine ran normally again. It ran normally during all the hard slogging
and half a tank of fuel the next two days (see my Late Fall Cruise post).

What do you think was going on? My guess is that the filters were both
clogged and the pressure cut off switch in the pump stuck after a long
period of working against the pressure. Cooling, vibration, or someone
sneezing in China unstuck the switch. The pump is now suspect and will be
replaced with another Steward Warner but you can bet that there will always
be a spare on board now.

I'm also suspicious about the little engine driven pump. This fuel system
is on the borderline of needing the electric lift pump. I wonder if maybe
the engine pump failed years ago and the electric was put into compensate.
Possibly the engine pump failed recently and the failure was masked by the
electric pump continuing to shove fuel through it. This extra work also
could have been a factor in the temporary shut down of the electric. I'll
pull the engine pump after winterizing the engine and see what the story is
there.

These things are seldom as straightforward as they seem.

--
Roger Long

First off, I've never heard of any engine manufacturer calling for a 2
micron filter as a primary, their way too restrictive, and can cause
problems with the supply pump. Typical application is a 30 micron
primary followed by the engine manufacturers secondary mounted on the
engine, which is probably a fine filter, but I suspect it's not as
fine as 2 microns. The manufacturer of my diesels, Cat, when you speak
to their field support guys, they will tell you, point blank, nothing
finer on the primary than a 30 micron, they will tell you anything
more than that is too restrictive and will cause the supply pump to
wear out faster as it is working that much harder to draw fuel into
the pump. The 30 micron filter catches the vast majority of the
contaminants, while continuing to allow the filter to flow enough fuel
to the supply pump. The 2 micron filter clogs too easily, causes
excessive restriction, with no real benefit. I know people like to
think if 30 microns is good then 15 must be better, 10 better still,
and 5 must be great, but that's just not how it works. Follow your
manufacturers specification, and you won't have to replace the pump
again.

John

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